WNC Orchard Insect Pest Populations – April 7, 2020
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This past weekend CALS administration granted the apple entomology program permission to begin our insect monitoring program in commercial orchards. Of course we will need to follow social distancing and sanitation practices to avoid transmission of the coronavirus. We set up some of our trapping sites today, which will help to improve our insect activity updates and recommendations.
While bloom is a time when the need for apple insect control takes a hiatus, scouting for green fruitworm feeding damage to new shoots should be conducted in a week or so to determine the need for control. The green fruitworm is a generic term that refers to a complex of three lepidopteran species of fruitworms that have comparable life histories and cause similar damage to apple. They are generally considered sporadic pests that do not occur every year. Since foliage feeding damage precedes fruit damage, scouting for damage can help determine the need for insecticidal control.
Description and Life History: There are at least three species of noctuid moths that are commonly referred to as green fruitworm on apple, with the speckled green fruitworm, the widestriped green fruitworm, and the humped green fruitworm being the most commonly encountered. These insects have a wide host range that includes deciduous shade, forest and fruit trees and shrubs. Some species, such as the humped green fruitworm, lay eggs in the late fall and larvae hatch near bloom. Other species emerge as adults in the early spring near green tip and lay eggs on twigs and leaves up to early bloom. Larvae feed on both foliage and fruit, with the damage to fruit occurring any time between early fruit set to first cover.
Damage: Many, but not all, apples damaged by green fruitworms abort. Some will remain through harvest and exhibit deep corky scars and indentations. Shown below is some fresh feeding on apple, some older scars on small fruit, and a file photo of damaged fruit at harvest.
Monitoring for GFW: Because green fruitworms are considered sporadic pests, it is advisable to monitor for their presence before making the decision to apply an insecticide specifically targeting them. Fruitworm larvae feed more on foliage than fruit, and feeding damage to foliage precedes damage to fruit. Hence, the presence of feeding damage on new shoot growth on early-maturing varieties can used as a guide to the presence or absence of larvae in an orchard.
Control: Damage to fruit can occur shortly after new fruit are formed, and before all petals have fallen off of a tree. Hence, the need to protect bees and delay petal fall sprays until late-maturing varieties have reached the true petal fall stage in orchards with multiple varieties can lead to increased levels of damage on earlier blooming varieties. Therefore the most effective approach to control green fruitworms is to apply an insecticide that is non-toxic to bees at early petal fall. The only two insecticides that meet the criteria of controlling fruitworm and being safe to bees are Intrepid (6 oz/acre) and a Bacillus thuringiensis product such as Dipel, Xentari or Agree.
Learn more about southeastern apple insect pests at the Apple Insect Management page.
2020 Average Weekly Trap Captures
|Insects per trap|
|Oriental Fruit Moth||0.0||7.5||24.5|
|Tufted Apple Bud Moth||–||–||–|
|Apple Maggot (abandoned and research)||–||–||–|
|Brown Marmorated Stink Bug (commercial – mountains)||–||–||–|
|Brown Marmorated Stink Bug (commercial – upper Piedmont)||–||–||–|
|Brown Marmorated Stink Bug (research – unsprayed)||–||–||0.3|
|Spotted Tentiform Leafminer||0.0||0.0||0.0|
|Lesser Peachtree Borer||–||–||–|
|San Jose Scale||–||–||0.0|
*Note that these averages illustrate only the timing of insect emergence and fluctuations in populations, and are not representative of population levels in any given orchard. The only way to have an accurate assessment of an individual orchard’s populations is to set up traps in that orchard.
2020 Accumulated Degree Days
|Oriental Fruit Moth||–||–||–||–|
|Tufted Apple Bud Moth||–||–||–||–|